1. Field of the Invention
The present invention relates to axially connected intraluminal segments and more particularly to individually expandable segments connected at least partially by fibers. In addition, the present invention relates to intraluminal devices, and more particularly to intraluminal devices, such as stents, incorporating fibers that operate as bridges axially connecting adjacent stent segments. The present invention also relates to stent structures having geometric features that serve as fixation points for the fibers described herein.
2. Discussion of the Related Art
Intraluminal devices have been known in the art for a number of years. These devices have utilized a variety of materials, but commonly fall into two broad categories; namely, self-expanding and balloon-expandable. Nickel-titanium is a common material selected for use in self-expanding device designs, while stainless steel and cobalt alloys have been common materials in balloon-expandable devices.
The flexibility of these devices is an important factor affecting delivery and performance within the body of the patient. A tortuous vascular anatomy requires a device to be able to conform to the anatomical conditions, before and after deployment, while preserving the device's primary functionality. Self-expanding materials provide superior flexibility relative to balloon-expandable materials for the specific reason that the self-expanding materials tend to conform to a tortuous anatomy with less tissue trauma than balloon-expandable materials. Examples of self-expanding intraluminal devices include stents, vena cava filters, distal protection devices, and occluders. However, maximizing the flexibility of intraluminal devices may lead to negative tradeoffs in other aspects of the device's mechanical performance, such as radial strength and buckling resistance. Additionally, in many cardiovascular applications, the device may be subject to significant dynamic deformations such as twisting, axial extension/compression and bending not seen in other parts of the vasculature. Under such conditions, a device should preferably be able to tolerate large dynamic deformations while remaining intact such that its primary functionality is preserved.
Radially expandable intraluminal devices commonly comprise a plurality of axially adjacent radially expandable segments. Such axially adjacent radially expandable segments are often joined by connecting elements generally described as bridges. In some cases, these bridge elements are not radially deformable, but rather are axially deformable, allowing for relative motion between axially adjacent radially expandable segments. This relative motion may desirably accommodate static or dynamic bending, stretching, or compression of the implanted device. The number of bridge elements present around the circumference of a design is an important design consideration. Fewer bridge connections allow for more flexibility and conformability, but potentially compromise scaffolding uniformity and vessel coverage. More bridge connections improve scaffolding uniformity, but potentially result in an undesirably stiff structure.
Radially expandable intraluminal devices are commonly fabricated such that the radially expandable segments and bridge elements are integral, or formed from a single continuous material, and therefore the finished device is a single contiguous structure.
The above described loading cases of bending, flexion, stretching, and compression create design challenges for flexibility and durability of intraluminal implants. One solution to these design concerns is to provide a design with fewer integral bridging elements, or ultimately no integral bridging elements, such that each segment is subject to only the localized forces and deformations at its immediate location. This design presents some difficulty in the precise placement of the individual segments within the target area of the lumen. Specifically, in the instance of self-expanding materials, the device is introduced in a constrained state within a sheath. As the constraint is removed from the self-expanding segment, the rapid increase in diameter creates axially directed forces which would tend to propel the segment forward in the absence of adequate axial constraint between the expanding segment and axially adjacent constrained segment still completely or partially within the sheath. In circumstances where the segment length is somewhat short in comparison to its diameter, this may result in the segment jumping forward from the distal tip of the delivery device, which in turn creates difficulty in the precise placement of the segment. Additionally, there is a need to provide a means for ensuring the uniformity and stability of adjacent segments during deployment. Accurate placement of intraluminal devices is of paramount importance to ensure that problems such as inaccurate placement over target lesions, distortion, or occlusion of critical branch vasculature does not occur.
In addition, intraluminal devices are a known means for the delivery of therapeutic agents to localized areas within the body of the patient. A common method for combining the delivery of therapeutic agents into the performance of an intraluminal device involves coating the surface of the device with a polymer containing the therapeutic agent. The surface area of the device becomes a limiting factor in the quantity of therapeutic agents that may be delivered. Coating the device with a polymer may also present difficulty in controlling coating adhesion, controlling coating thickness, and controlling coating interaction with the therapeutic agent. Consequently, increasing the available surface area of the device without sacrificing its mechanical performance and flexibility, or eliminating the need for coating the device surface may simplify the manufacture and efficacy of such devices.
Accordingly, there exists a need for intraluminal devices that that avoid the problems described herein.